Reapers of Sidonia
by Masamune3800
Summary: This is a crossover between Knights of Sidonia and Bleach, more information on how the universes interact will be explained throughout the story. Contains OCs.


A/N: Hello and welcome to my fourth story, a crossover between Bleach and Knights of Sidonia. After learning my lesson from my previous two crossovers, I am not going to spend three thousand words trying to explain how everything in this universe will work; instead I am going to show you through the story. In addition, I will be re-introducing all of my OCs as though I have never used them before. For anyone who already knows about my OCs try to bear with me here, I want to try and give everyone the chance to get to know my characters from scratch instead of trying to guess based on random hints I drop.

I know I just said that I would avoid lengthy explanations in the first A/N this time, so I will just give you one small little detail that is fairly important; Heigus/Higgs/Hyggs particles are going to be replaced with Reishi (Spirit particles in Bleach). This will have almost zero impact on the operation of the various technologies in the Knights of Sidonia universe and is more a thematic change than anything else. As for why I decided to do that, you will find out eventually but the first bunch of chapters will be in a universe that is almost exactly the same as the Knights of Sidonia universe. As a final note, I am only going off of information given in the anime series, the plot of this story may well completely split off from where the manga went and develop into something entirely different. This is mostly to avoid spoiling anything for people who haven't read the manga; I don't want to be 'that guy'.

With that my explanation is over, I hope you enjoy this story, and if you do like my OCs feel free to check out some of my other stories since the OCs are mostly a constant.

Disclaimer1: I only own the boring kind of bleach…  
Disclaimer2: I don't own Knights of Sidonia…

Reapers of Sidonia

Chapter 1

* * *

Rein slowly allowed his eyes to open to the dull grey ceiling in his cramped dorm room. He felt a fit of shivers coming on and reached down to the floor where his blanket had fallen as he slept and wrapped it around his body. Once the shivers had subsided he lifted himself off of his bed and reached into his closet, retrieving a uniform for the Sidonia Defense Force Academy and changing into it. Rein walked over to the mirror next to his door and checked over his appearance to make sure he didn't forget anything important. He was one-hundred-eighty-eight centimeters tall and fairly thin with moderately pale skin. His eyes were a bright shade of blue but otherwise were completely normal. Satisfied he reached up to a hook behind him and grabbed a black coat and a scarf of the same color as his eyes, which he wrapped tightly around his neck and chin. Obviously the temperature of the seed ship was closely regulated to be comfortable for its inhabitants, but Rein was an exception. Ever since he could remember he had been extremely sensitive to even the slightest change in temperature, according to a doctor he had visited a drop of even a few degrees Celsius in outside temperature for an extended period of time would be enough to risk hypothermia so Rein tended to dress warmly to be on the safe side. He glanced in the mirror once more and ran his hand through his short black hair to get it back to his preferred level of spikiness before walking out his door.

Not much later Rein stepped into the dorm cafeteria, which was mostly empty today. The majority of the other students at the Sidonia Defense Force Academy had synchronized the one day per week that they spent eating. Rein was slightly different; though he was fully capable of photosynthesis his efficiency was significantly lower than other humans, he had to eat once every four days. Luckily for Rein, he did not have to eat alone. After he had gotten some food he walked over to a table that contained his two siblings. His brother, Anima, was seventeen, one year younger than Rein. He was one-hundred seventy-six centimeters tall and had a similar build to his older brother. His hair was a dark purple and it reached to his shoulders while his eyes were a deep navy blue. Across from Anima sat Tsume, who was sixteen. She was much shorter than her brothers at one-hundred-forty-eight centimeters and was also of slim build with subdued curves. Her hair was dark grey and her bangs fell down on the right to cover one of her bright blue eyes with slit pupils.

"Morning." Rein sat down next to Tsume and greeted his siblings. They had been very close since they were born, mostly due to their parents. Rein did not know too much about their parents, only that they had subjected him to quite a few experiments before and after he was born. He had been told that the details of the experiments were something that he was better off not knowing, but they were the cause of his 'defects' in both internal temperature regulation and photosynthesis. Apparently Tsume had been subjected to the same sort of experimentation as Rein had been but luckily there did not seem to be any major problems with her physiology. Anima was the only one who had been spared from the horrors their parents had decided to put them through.

"Morning Rein." Tsume said cheerfully as she watched him eat "Did you sleep well?"

Rein shrugged "Can't complain." He shoved the rest of his food down his throat "Come on, we will be late for class."

* * *

Rein, Anima, and Tsume walked into the circular classroom and took their seats near the middle. In the center of the room was a fairly tall man with short white hair and bright green eyes. He was one of -if not the only- person remaining on Sidonia who chose to wear glasses. To most of the students in the room he was known as their teacher, Kyokan. To Rein, Anima, and Tsume he was known as their guardian. He had taken care of the trio ever since they had been abandoned by their parents a few months after Tsume had been born. Kyokan was also the one who had helped Rein find ways to deal with his 'defects' and told them a bit about what their lives had been like before they met him.

"Ok, class will begin now." Kyokan stated, drawing the attention of everyone in the class "As I hope all of you know exams will be starting in a few weeks. In order to prepare each class from now until exams will be entirely dedicated to review. Since this is the first review session we will be going over the basics." He paused "First, can anyone tell me what a Gauna is?" A few hands shot up and Kyokan pointed at one of the students.

"A Gauna is an extraterrestrial being. It is composed of two parts, the core and the placenta; the placenta can be shaped into nearly anything and can regenerate with unbelievable speed. The core is the central part from which the placenta grows, it is indestructible to anything other than a Kabi and its contents are unknown." The student answered.

"Perfect response." Kyokan complimented "Yes, Gauna are the enemies of humanity as a species and the reason all of you are here training. Next question, how does a Garde Frame work?" Once again a series of hands shot up from the students and Kyokan selected one to answer.

The student stood up "A Garde Frame is a mechanized suit used to combat the Gauna. Its fuel source is stored Reishi which is converted by the pilot into Reiatsu and then used to power all of the Garde's functions."

"Very good, now can someone tell me how this Reishi Conversion works?" Kyokan asked, selecting a student to answer yet again.

"Reishi is extracted from its storage tanks and mixed in with the air breathed by the pilot. After the Reishi is absorbed by the pilot's body it is emitted by the pilot with varying levels of efficiency as a form of radiation known as Reiatsu. The Reiatsu is then absorbed by panels on the interior of the Garde Frame's cockpit." The student responded.

"Yes, and how can a pilot increase his or her Reishi Conversion Efficiency?" Kyokan questioned, this time he selected Anima to answer.

Anima stood up "The baseline value varies from pilot to pilot but tends to increase with the pilot's concentration levels."

After about two hours of review Kyokan spoke "Ok, we will take a break from review and head to the simulation room."

* * *

The students walked into the simulation room. In the center there were a total of ten simulators which would allow each of the one-hundred students in the class to get their chance within an hour. On the wall behind them was a large scoreboard that displayed the top ten scores for this session as well as the previous session. Below the board was a terminal that would allow anyone to quickly look up their own score history as well as more detailed records of each individual simulation session. Currently the large scoreboard was blank, waiting for this session's top ten students to be determined.

Soon it was Rein's turn to enter the simulator; he stepped into the mock cockpit and entered a sequence of commands to start the simulation machine. After he had entered his name and the system verified his identity a short message appeared on the screen.

Welcome to the Type 18 Garde Frame training simulation.  
Identity confirmed as Masamune Rein.  
Note: Due to instructor request simulation rate has been increased to 'X2'.

Rein smirked at the last sentence, ever since his first few tries in the simulator Kyokan had kicked up the difficulty setting for him by doubling the tick speed of every detail in the simulator from the performance of his Garde Frame to the Gauna he fought. This wasn't so much of a handicap as it was a leveling of the playing field to eliminate his natural advantage.

Yes, he had a natural advantage in the simulation. The truth was that one of the experiments his parents had performed on him had worked out correctly; his brain was capable of functioning at double the rate of an ordinary human. Effectively everything that happened around him was viewed by him at half the speed that other people experienced. He honestly didn't mind the significant increase in the simulation's difficulty; Rein would never be able to improve himself if every run through the simulation was a cakewalk for him.

Soon the familiar smell of Reishi infused air began to fill his nostrils and he felt a momentary surge of elation as the foreign substance reached his brain. The sensation quickly dissipated when his body automatically began to process the Reishi into Reiatsu and he regained his focus. Rein looked over to a small monitor in the corner of the cockpit that displayed the efficiency at which he was converting the Reishi into Reiatsu. Currently the number was fluctuating around the mid-twenties so he put some more effort into the conversion until the number peaked at fifty percent. Satisfied Rein reached forward and pressed a button to begin the simulation.

* * *

The array of screens in front of Rein flickered to life, displaying a nearly perfect image of what it would be like to pilot a Garde Frame in open space. Judging by the sight in front of him this was clearly not one of the urban combat simulation missions so he waited for the simulation to give him instructions. He didn't have to wait long; soon a message appeared on one of his monitors accompanied by a clearly artificial female voice "A Gauna has been detected approaching the Sidonia. Your mission is to keep it from entering a certain radius of the ship displayed on your digital map. Destruction of the Gauna is not a requirement for success, long range combat is suggested."

Rein let out a groan, this mission was the most annoying of any simulation, not because the goal was particularly hard but because the direction that the Gauna would approach from was randomly determined along with the location that your Garde Frame would be when the simulation started. If you were particularly unlucky you would be on the exact opposite side of the Gauna and even if you pushed your engines to their limit the maximum amount of time you would have to deter the Gauna would be about thirty seconds, barely enough time to open a hole through is placenta. Soon his digital map was updated with the location of the Gauna and Rein rushed over to intercept it, all the while thanking whatever deities existed that he had been placed relatively close to his objective.

Soon he was within range to see the Gauna with his own eyes; it was not anything too complex this time, just a ball with a large array of tentacle like protrusions around it. Rein gave the situation a few moments of thought before he came up with a plan of action. The AI used to simulate a Gauna was programmed to avoid Kabi as its first priority; the weight given to that objective was so high that a Gauna in a simulation would willingly fly directly into the path of multiple Reiatsu beams just to avoid the material. Rein decided to take advantage of that behavior and gripped the Kabizashi upside down in the left hand of his Garde Frame and hurled it with quite a bit of speed into the path of the oncoming Gauna. As soon as the spear left his hand he leaned the Garde Frame forward and spiked his Reishi conversion up to about fifty-one percent, directing all of the power to the massive engine on its back. He shot forward with all the speed at his disposal, ignoring the warning light that appeared to notify him that his Reiatsu output was not high enough to maintain his current speed for more than a few seconds. He knew his own limits and the limits of his Garde Frame well enough to be sure that his plan would work. Once he was in firing range of the Gauna he turned the engines down to normal output again and fired his Reiatsu Cannon slightly off to the side of where the Gauna was currently heading. As he predicted the Gauna detected the oncoming Kabizashi and shifted its flight path upwards to avoid the Kabi tipped spear. Just as it finished its maneuver a beam of highly concentrated Reiatsu slammed into its placenta, revealing its core. As soon as the beam had fired Rein turned his engines back to full power, easily surpassing the speed of the Kabizashi he had thrown barely ten seconds earlier and gripping it in his left hand once again as he passed it. Once the spear was in his possession again he shifted his course slightly and aimed the spear out in front of him, allowing it to pierce the exposed core of the Gauna as he passed by. The moment Kabizashi made contact the core of the Gauna began to foam and dissolve along with the placenta and a message appeared in the center of his monitor.

Mission Complete.  
You may view your score at the end of the simulation session.

The images on the monitors faded along with the scent of the Reishi infused air. Rein quickly logged out of the simulator and stepped into the room once again to allow someone else to use the machine.

* * *

After the last student had finished their mission they all turned their attention to the large scoreboard behind them, a set of ten names and scores appeared on the screen.

Place Name Score Previous Score RCE (Reishi Conversion Efficiency)  
01: Kunato Norio 27306 26408 41%  
02: Masamune Rein 26842 26601 46%  
03: Hoshijiro Shizuka 23880 22101 38%  
04: Masamune Tsume 23107 22034 42%  
05: Honoka En 21063 20304 37%  
06: Senna 20836 16012 40%  
07: Honoka Hou 19443 18764 36%  
08: Honoka Ren 19105 18509 36%  
09: Masamune Anima 18704 17402 35%  
10: Tsuin Tachikiru 18532 17320 34%

He quickly looked through the scores, clearly Tsume was still having issues adapting to the accelerated speed training. Since she had been subjected to the same sort of experiments Rein had been she also was able to make her brain function faster than an average human. Her biggest issue is that it wasn't consistent, the speed boost to her brain tended to fluctuate between ten and thirty percent faster, Kyokan had gotten tired of adjusting it every week and had just set her speed modification to 'X1.3'. What really caught his eye was the new addition to the top ten, a girl named Senna. Just a few days ago her score had been in the sixteen-thousands but now it had jumped up to nearly twenty-one thousand. She had completely knocked Eiko Yamano out of her usual tenth place and planted herself right in the middle of the Honoka sisters with sixth place. In addition, her RCE was nearly as high as Tsume's; Rein considered finding her to congratulate her but his thoughts were interrupted by a voice behind him.

"Looks like I came out on top this time Rein." He recognized the voice as belonging to Norio Kunato, a tall boy with long white hair.

Rein turned around "Yeah, you nearly managed a one-thousand point jump this time, nice work." Rein was not a competitive person by nature; Norio on the other hand was not satisfied unless he was the best. Rein tended to just play along with him because he knew that it was the sort of environment that someone like Norio would thrive in. A bit of competition was usually the best way to improve your skills. Rein smirked a bit "Don't get too confident Norio, next session I will step up my game."

"Good, it wouldn't do for you to start slacking off." Norio cracked a nearly unnoticeable smile, which surprised Rein. Norio Kunato was well known for three reasons, first was that he was the head of the Kunato Family and thus ran the Kunato Developments company which was in charge of producing the newest model of Garde Frames, the Type 18. Second, he aggressively tried to maintain his position at the top of the rest of the students, him and Rein were regarded to be on equal skill levels and would often alternate between the first and second positions quite rapidly. The third thing Norio was known for was that he never smiled under any situation. Rein knew that most rumors of that nature were exaggerations, but he had not once seen Norio produce a real smile, he usually just kept to condescending smirks when he was at the top of the list and annoyed scowls when he was not at the top.

Kyokan ended all of the smaller conversations going on around the simulation room the moment he began speaking "Well done everyone, considering that exams are coming up I will leave the simulation room open for the rest of the day so you can hone your skills a bit more. This concludes today's classes."

Once Kyokan had finished speaking Rein looked around at his surroundings again, noting that Norio had ran off while Kyokan was speaking. Just as Rein began to leave the room he felt a hand on his shoulder, once again he turned around to find Norio standing behind him. This time Shizuka Hoshijiro, the third place, was with him.

"Hey Rein; you want to come hang out with us for a bit?" He asked.

Rein looked around the room quickly, after seeing that both his siblings seemed to be leaving with their own friends he turned back to Norio "Sure, sounds like fun." He was placed into shock yet again by Norio's behavior; he was acting much more cheerful than he usually did. Rein glanced at Shizuka, wondering if she might have something to do with it. Judging by the confused and awkward expression on her face she was as lost as he was so they clearly hadn't begun dating or anything of the sort. Rein let his thoughts drop and followed Norio out the door with Shizuka.

Not much later they were standing on a walkway between two sections of the Sidonia Defense Force Academy. On the inner side of the walkway rested the legendary Type 17 Garde Frame Tsugumori. The very same one used by the pilot Ace in the defense of Sidonia against two Gauna that had breached the ships defenses.

Norio stopped in front of the frame and looked at the plaque below it "It is my dream to one day pilot this Garde Frame and protect Sidonia."

"It's good to have a dream." Shizuka commented quietly, also reading the plaque.

Rein frowned going through his memories and recalling what the differences were between the older Type 17 and newer Type 18 Garde Frames. The first distinction that came to mind was that the Type 17 was manufactured by Toha Heavy Industries while the Type 18 was created by Kunato Developments. Although Rein found it odd that the heir to Kunato Developments had the dream of piloting a frame made by his own companies main competitor he moved on to the next difference, the Type 18 had many additional autopilot features to make it easier to pilot compared to the Type 17, which relied entirely on the competence of its pilot to perform complex maneuvers. The final distinction was that the Type 18 did not allow the pilot to adjust the concentration of Reishi in the air that they breathed. This change was made mostly to avoid potentially lethal cases of Reishi Addiction, where Pilots would begin to lose focus due to their bodies being unable to convert the Reishi into Reiatsu fast enough to keep it from building up in their blood. The major downside to this was that being unable to modify the Reishi concentration limited the capabilities of more experienced pilots who were able to convert Reishi into Reiatsu much more quickly and efficiently than novice pilots. Other than a few minor design changes that was all that varied between the Type 17 and Type 18 Garde Frames. Based on that information many newer pilots thought of the older model as a more high performance frame and that the newer Type 18s had 'clipped wings' so to speak. In reality unless someone had spent their entire life training on a Type 17 it would do nothing more than create unnecessary risks to their life.

Rein noticed that he had spent a bit too much time thinking and quickly responded to dispel the tense atmosphere "Well, I would prefer to stick with the Type 18, mostly because I have never met someone from Toha Heavy Industries and I trust you, Norio."

Their conversation was interrupted by another group of trainees opening the door on the opposite side of the walkway. Rein noticed his younger sister Tsume, Senna, Eiko Yamano, a person he did not recognize, and three of the Honoka Sisters. He had long since given up on distinguishing any individual member of the eleven identical sisters and tended to just wait for them to identify each other over the course of a conversation.

Eiko stepped out in front of the group and turned around "Can't you guys take things more seriously? We have exams coming up soon and you want to go explore the ship?" Seeing no response from the group she just turned and stormed away.

Tsume waved to Rein "Hey Rein, you want to join us?"

He glanced back at Norio and Shizuka as though looking for approval.

"Go ahead Rein, I would be worried if my sister decided to go and randomly explore the ship too." Shizuka encouraged, Rein nodded and walked over to Tsume and her friends.

"What made you suddenly want to go exploring?" Rein asked curiously, following the group off of the walkway.

"You haven't heard?" One of the Honoka Sisters said in a surprised tone, her shoulder length pink hair shifting slightly as she turned to face Rein.

"Heard about what?" Rein questioned.

"The Mole Man." Senna said as though that explained everything.

Tsume sighed "Apparently someone snuck into the Rice Thresher from underground and managed to injure himself, Ren said she knew which hospital he was in so we were going to go try and visit him."

Rein nodded, he hadn't heard about anyone sneaking up from underground but the possibility was certainly there. The underground tunnels in Sidonia were said to be akin to a complex labyrinth, once you entered it was nearly impossible to find your way out. Pretty much anything could be living down there without anyone knowing about it "Sure, sounds interesting."

The group entered an elevator heading down to the level that contained the hospital they were heading to. On the way down Tsume spoke "Oh right, you haven't met Izana." She gestured to the person Rein hadn't recognized.

Izana smiled "My name is Izana Shinatose. Before you ask, I am not male or female; I'm of the third gender, nice to meet you."

(A/N: Ok, so the English language tends to get pretty clunky when you start trying to use words like him, her, his, hers, he, and she on a genderless person so to make life easier I will use the female versions of the words to describe Izana. I decided to go with the female versions because Izana's voice actor is female, overall it doesn't matter too much so if it bothers you try to ignore it.)

"Nice to meet you as well." Rein replied. There was indeed a third gender on the seed ship; essentially their body would develop into one of the two standard genders once they had chosen a partner. It was one of the solutions that genetic engineers came up with to deal with the population loss during the Fourth Gauna Defense War just like human photosynthesis was a solution to the food shortages.

"Oh, right." Rein said as though remembering something "Congratulations on managing to jump up four-thousand points in your score for the simulation Senna, I was really shocked."

"Thanks." Senna smiled "I don't know how I did it; I guess everything just sort of clicked into place."

* * *

After a few more minutes the group had arrived on the floor where the hospital that the 'Mole Man' was staying in was located. Said hospital was around ten meters in front of them on the right, on the other side of the pathway there was a hunched-over old man holding up a sign and calling out protests to people passing by "Stop the militarization, end martial law, the Gauna are gone."

Rein frowned; something about the man's protesting just wasn't sitting right with him. As they got closer Rein moved over to the side of the pathway that the man was occupying. When they were within two meters of the protestor Rein walked up to him and spoke "Look, I get that we haven't seen a Gauna in around one-hundred years, but that doesn't mean they are gone."

"The Gauna are just an excuse used by the government to gain more power." The man shot back.

"Even if they are, the military does more than simply fight Gauna. They also run supply retrieval operations, without them all of us would have died a long time ago." Rein replied calmly.

The man seemed to ignore Rein's arguments, instead shouting out to other passersby "See, the military has even gotten to the younger generations, there is no hope for Sidonia!"

Tsume pulled Rein away "Just let it go Rein, it doesn't matter."

Rein nodded "Right."

Without any warning the glass in one of the upper floors of the hospital they were visiting shattered and a person who looked about their age jumped out, landing roughly on the ground right in between Norio and Shizuka, who were also passing by. Someone stuck their head out the window that had been broken "Someone stop him!"

Norio frowned and slammed his fist into the boy's face just as he was beginning to stand up, knocking him out. The crowd around them collectively winced, knowing that the punch must have hurt quite a bit.

Rein heard Shizuka sigh "I will bring him to the police." She bent down and picked the boy up, beginning to walk in the direction of the nearest police station.

* * *

Words: 4,474 (Without A/Ns, I usually average around 4,000 words a chapter)

A/N: Hope you liked the first chapter of my new story, let me know if you have questions of any kind and I will get back to you as soon as I can.


End file.
